03 June 2010 (Koenraad): contacted Interkontakt (Dutch firm) for pricing on their connectors

TODO: Make a pin-out

HALL sensors

Each module has two hall sensors to detect the position of the rotating magnet (x- and y-axis). These are old chips, and no datasheet seems to exist on the internet.
The best we could find is the following:

DC motor

The motor drives the flaps and the magnet. The mechanics of the wheels prevent it from going backwards.

TODO: Determine specs

Flap slots

There are 60 slots on the module we currently have, each carrying a flap with half a character on both sides.

TODO: Is the number of slots the same for all of them?
TODO: Size of flaps for cutting our own from plastic sheets

Character sequence on the unit we have:

White A-Z

Big -

Small -

/

Space

Red A-Z

Red Ö

Red Large -

Red Small -

Space with a small white dot

Preliminary ideas for a prototype and the display

It is pretty clear that we first have to figure out how everything works before being able to make a large display. Unless we can get specifics from someone that knows more about these displays, we will first need to learn how to drive one module.

Some loose ideas:

Wires can be soldered to the control board to save money if needed. Drop some hot glue over them for solidity.

We only need the motor to go in one direction. Thus, a full H-bridge is not neccesairy, and one FET with a freewheel diode will do

We need only 3 signals per module, nl. motor+, hall1_out and hall2_out. PWR, GND and motor- (=GND) are shared between all modules

So we need 2 analog ins and one digital out for one module

The digital out can be multiplexed into a row/column configuration, so we really need only 2 sqrt(n) digital pins for n modules

The analog pins can be multiplexed by time-division multiplexing, but we will need extra digital pins for this. Total: 1 analog_in and 2 sqrt(2n) digital pins, or 2 analog_in and 2 sqrt(n) digital (both are equivalent)

These requirements can be reduced even further since from sqrt(n) pins only one will be selected at a time. Using three 4-bit demuxing chips (74XX154), we reduce the number of GPIO pins to 4*3 = 12, or less if we use a bus protocol.

So it is indeed possible to control the entire display from one control board!